In a liquid crystal display apparatus such as a liquid crystal display television using a plurality of discharge tubes in a single panel of a liquid crystal screen, it is necessary to illuminate the entire liquid crystal screens in uniform luminance from the discharge tubes. If the plurality of discharge tubes are lighted (turned ON) in different current values, an illumination failure such as unequal luminance gradations may occur. FIG. 10 shows a multi-discharge tube lighting apparatus for applying AC high voltages (alternating high voltages) to one terminal of each of a plurality of discharge tubes so as to balance currents flowing through the respective discharge tube. As shown in FIG. 10, the multi-discharge tube lighting apparatus includes: 3 sets of discharge tube units 1 to 3; an AC power supply 10; transformers T1 to T3; another transformer T4; and still another transformer T5. Each of the three discharge tube units 1 to 3 includes: a first discharge tube 1a and a first winding 1b, which are series-connected to each other; and a second discharge tube 2a and a second winding 2b, which are series-connected to each other. One terminal of each of the first discharge tubes 1a and each of the second discharge tubes 2a is connected to the AC power supply 10 via a capacitor 20. In each of the transformers T1 to T3, the first winding 1b is electromagnetically coupled to the second winding 2b. In the transformer T4, a first winding 1b is electromagnetically coupled to a second winding 2b, where the first winding 1b is connected to both the first winding 1b and the second winding 2b of the transformer T1, and the second winding 2b is connected to the first winding 1b and the second winding 2b of the transformer T2. In the transformer T5, a first winding 1b is electromagnetically coupled to a second winding 2b, where the first winding 1b is connected between the first and second windings 1b, 2b of the transformer T4 and the ground, and the second winding 2b is connected between the first and second windings 1b, 2b of the transformer T3 and the ground. The current flowing through the discharge tube 1a and the current flowing through the discharge tube 2a of the first discharge tube unit 1 which is connected between the AC power supply 10 and the ground via the capacitors 20 and the transformer T1 is balanced by the first winding 1b and the second winding 2b of the transformer T1, so that the same current flows through the discharge tubes 1a and 2a. The total current of the two discharge tubes, i.e., the first discharge tube 1a and the second discharge tube 2a, flows through a junction point between the first winding 1b and the second winding 2b of the transformer T1.
Similarly, the current flowing through the discharge tube 1a and the discharge tube 2a of the second discharge tube unit 2 connected between the AC power supply 10 and the ground via the capacitors 20 and the transformer T2 is balanced by the first winding 1b and the second winding 2b of the transformer T2, so that the same current flows through the first discharge tube 1a and the second discharge tube 2a. The total current of two discharge tubes, i.e., the first discharge tube 1a and the second discharge tube 2a, flows through a junction point between the first winding 1b and the second winding 2b of the transformer T2.
Similarly, the current flowing through the discharge tube 1a and the discharge tube 2a of the third discharge tube unit 3 connected between the AC power supply 10 and the ground via the capacitors 20 and the transformer T3 is balanced by the first winding 1b and the second winding 2b of the transformer T3, so that the same current flows through the first discharge tube 1a and the second discharge tube 2a. The total current of two discharge tubes, i.e., the first discharge tube 1a and the second discharge tube 2a, flows through a junction point between the first winding 1b and the second winding 2b of the transformer T3.
The junction point between the first winding 1b and the second winding 2b of the transformer T1 is connected to the first winding 1b of the transformer T4, and the junction point between the first winding 1b and the second winding 2b of the transformer T2 is connected to the second winding 2b of the transformer T4. Therefore, the current flowing through the first discharge tube unit 1 and the second discharge tube unit 2 is balanced by the transformer T4, so that the same current flows through the first discharge tube unit 1 and the second discharge tube 2. The total current of the four discharge tubes, i.e., the discharge tubes of the first discharge tube unit 1 and the second discharge tube unit 2, flows through the junction between the first winding 1b and the second winding 2b of the transformer T4. The current of two discharge tubes, i.e., the third discharge tube unit 3, flows through the junction between the first winding 1b and the second winding 2b of the transformer T3.
The junction point between the first winding 1b and the second winding 2b of the transformer T4 is connected to the first winding 1b of the transformer T5, and the junction point between the first winding 1b and the second winding 2b of the transformer T3 is connected to the second winding 2b of the transformer T5. As a consequence, the current flowing through 4 pieces of the discharge tubes flows through the first winding 1b of the transformer T5, whereas the current flowing through 2 pieces of the discharge tubes flows through the second winding 2b of the transformer T5, so that a turn ratio of the first winding 1b to the second winding 2b is set to such a value obtained by multiplying the flowing current by an inverse number. For instance, the current for the 4 discharge tubes flows through the first winding 1b of the transformer T5, whereas the current for the 2 discharge tubes flows through the second winding 2b thereof. As a result, a ratio of the current becomes a relationship of 2:1. As a consequence, assuming now that a turn number of the first winding 1b of the transformer T5 is equal to 1, a turn ratio of the first winding 1b to the second winding 2b of the transformer T5 is set to be 1:2, namely, a turn number of this second winding 2b is set to 2. Any of these transformers T1 to T5 have an effect capable of averaging and balancing the current flowing through the respective discharge tubes 1a and 2a. 
A multi-discharge tube lighting apparatus shown in FIG. 11 has a configuration that the capacitors 20 are omitted from the above-described multi-discharge tube lighting apparatus shown in FIG. 10. Another multi-discharge tube lighting apparatus shown in FIG. 12 has a configuration that the transformers T1 to T5 are omitted from the above-explained multi-discharging tube lighting apparatus, the first discharge tube 1a and the second discharge tube 2a of each of the first to third discharge tube units 1 to 3 are directly connected to each other to have a U-shape. Although the first discharge tube 1a and the second discharge tube 2a of each of the discharge tube units 1 to 3 are connected to one terminal and the other terminal of an AC power supply 10 which generates AC voltages having opposite phases to each other, this multi-discharge tube lighting apparatus of FIG. 12 cannot average and balance the current flowing through the respective discharge tube units 1 to 3. FIG. 13 shows another multi-discharge tube lighting apparatus. In the multi-discharge tube lighting, series-connected first and second windings 1b, 2b connected to each of the discharge tubes 1a and 2a are connected to a common line 4. The first winding 1b of the first discharge tube 1a of the first discharge tube unit 1 is electromagnetically coupled to the second winding 2b of the second discharge tube 2a of the third discharge tube unit 3 connected via the common line 4 to the first winding 1b of the second discharge tube 2a of the third discharge tube unit 3. Each of the first windings 1b of the second and subsequent discharge tube 2a of the first discharge tube unit 1 is electromagnetically coupled to the second winding 2b which is connected to the pre-staged discharge tube. That is, conversely, each of the second windings 2b is electromagnetically coupled to the first winding 1b connected to the post-staged discharge tube. FIG. 14 shows a configuration of another multi-discharge tube lighting apparatus in which the capacitors 20 shown in the lighting apparatus of FIG. 13 are omitted.
FIG. 15 shows another multi-discharge tube lighting apparatus. In the multi-discharge tube lighting apparatus, a first discharge tube 1a and a second discharge tube 2a of each of first to third discharge tube units 1 to 3 are respectively connected to one terminal and the other terminal of an AC power supply 10. A second winding 2b connected to the first discharge tube 1a of the first discharge tube unit 1 is electromagnetically coupled to a first winding 1b connected to the second discharge tube 2a of the first discharge tube unit 1, and this second winding 2b is connected to a common line 4. The first winding 1b connected to the second discharge tube 2a of the first discharge tube unit 1 is series-connected to a second winding 2b electromagnetically coupled to a first winding 1b connected to the first discharge tube 1a of the second discharge tube unit 2, and this second winding 2b is connected to the common line 4. Accordingly, FIG. 15 shows such an arrangement that a series circuit of the first winding 1b and the second winding 2b is connected between the common line 4 and the discharge tubes 1a and 2a of each of the first to third discharge tube units 1, 2, 3; each of the first windings 1b thereof is electromagnetically coupled to the second winding 2b of the pre-staged discharge tube, that is, each of the second windings 2b is electromagnetically coupled to the first winding 1b of the post-staged discharge tube. FIG. 16 shows another multi-discharge tube lighting apparatus in which the capacitors 20 shown in the lighting apparatus of FIG. 15 have been omitted. The multi-discharge tube lighting apparatus shown in FIG. 13 to FIG. 16 can average and balance the current in a similar manner to those shown in FIG. 10 and FIG. 11. The discharge tube lighting apparatuses capable of averaging and balancing the current in the above-explained manners is disclosed in, for instance, JP-A-2004-335443.
In a lighting apparatus for lighting a large number of discharge tubes, current flowing through at least one discharge tube in a single discharge tube unit can be balanced. However, in order to balance the current with respect to discharge tubes of other discharge tube units, it is necessary to provide transformers for balancing the current. As a consequence, in the above-described discharge tube lighting apparatus containing two discharge tubes in each discharge tube unit, a plurality of transformers are necessarily required, the total number of which is equal to twice number of the discharge tube units or equal to the number calculated by subtracting 1 from the twice number of the total number of the discharge tube units. As a result, costs of the discharge tube lighting apparatus may be increased.